Rocker arm assembly for the rear derailleur of a bicycle

ABSTRACT

Rocker arm assembly for the rear derailleur of a bicycle, comprising an outer plate ( 12 ) carrying a pivot pin ( 32 ), an inner plate ( 10 ) and a pair of idle transmission wheels ( 14 ) arranged between the outer plate ( 12 ) and the inner plate ( 10 ). The inner plate is made of metallic material and the outer plate is made of a structural fiber fabric incorporated in a thermoplastic material matrix.

CROSS REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/994,718, filed Nov. 28, 2001, which is/are incorporated byreference as if fully set forth.

BACKGROUND

[0002] The invention relates to a rocker arm assembly for the rearderailleur of a bicycle. The rocker arm assembly comprises an outerplate carrying a pivot pin, an inner plate and a pair of idletransmission wheels arranged between the inner plate and the outer plateand intended to co-operate with the chain.

[0003] The field of components for competition bicycles is characterizedby continuous research aimed at reducing the weight of single componentswithout compromising performance, particularly in terms of structuralresistance.

[0004] In rocker arm assemblies of the known kind, the front plate andthe rear plate are both made of light metallic alloys and arereciprocally fastened by means of screws which define the rotation axesof the transmission wheels. The use of different materials that wouldprovide a reduction in weight often puts problems in terms ofmaintaining structural resistance characteristics. Furthermore, theproblem related to the dimensions of the plates of the rocker armassembly cannot be neglected since this unit is arranged very close tothe spokes of the wheel, when the chain meshes the pinion which isclosest to the wheel.

[0005] In order to overcome the aforesaid drawbacks, the inventionrelates to a rocker arm assembly having the characteristics describedherein.

SUMMARY

[0006] The rocker arm assembly according to the invention ischaracterized in that the inner plate is made of metallic material andthe outer plate is made of a structural fiber fabric incorporated in athermoplastic material matrix.

[0007] This solution provides high stiffness and small thickness of theinner plate which is more affected by problems of occupied space toprevent interference with the wheel. The outer plate has less problemsof stiffness and occupied space and can be made of a lighter material,for example a composite carbon fiber-based material. Considering thatthe inner plate is made of metallic material, it can be provided withthreaded holes as in the traditional solutions, for engaging thethreaded ends of the screws defining the rotation axes of thetransmission wheels. If the inner plate were also to be made ofstructural fiber fabric incorporated in resin, the problem of making theplate thicker would arise to ensure the same resistance to flexion andthe increased thickness would cause an interference with the spokes ofthe wheel. Furthermore, making threaded holes in fiber fabricincorporated in a plastic material matrix would not be possible andthreaded metallic inserts would have to be used. This would increase theproblem of occupied space of the inner plate.

BRIEF DESCRIPTION OF THE DRAWING(S)

[0008] The invention will now be described, by the way of example only,with reference to the accompanying drawings wherein:

[0009]FIG. 1 is an exploded perspective view of a rocker arm assemblyaccording to the invention, and

[0010]FIGS. 2, 3 and 4 are cross-sections according to lines II-II,III-III and IV-IV in FIG. 1, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0011] With reference to the drawings, FIG. 1 illustrates the rocker armassembly comprising an inner plate 10, and outer plate 12 and a pair oftransmission wheels 14. The plates 10, 12 are fixed in a conventionalway by means of a pair of screws 16 which extend through respectivenon-threaded holes 18 of the outer plate 12 and engage respectivethreaded holes 20 of the inner plate 10. In a conventional way, thescrews 16 define the rotation axes 22 on which the transmission wheels14 are freely rotationally mounted. Respective bushings 24 areinterposed between the screws 16 and the wheels 14.

[0012] According to the invention, the inner plate 10 is made ofmetallic material, preferably aluminum or aluminum alloys, while theouter plate 12 is made of a structural fiber fabric incorporated in aplastic material matrix.

[0013] Preferably, the fabric is a carbon based fabric and the plasticmaterial is preferably of the thermosetting type. The outer plate 12 ismade by compression moulding of sheets readily available on the market,consisting of sheets of structural fibres coated with thermoplasticresin. During moulding, the outer plate assumes the definitive shapeillustrated in the figures, with a transversal cross-section shaped as ashallow channel, as illustrated in FIGS. 3 and 4, to increase theflexion and torsion stiffness. The holes 18 for the screws 16 andlightening holes 26 are formed during moulding. Preferably, an integralelement 28 made of plastic material projecting from a an outer face ofthe outer plate 12 is also formed during moulding. The element 28carries a freely rotating worm screw 30.

[0014] A hollow pin 32 of metallic material, preferably steel, isfastened by caulking in a hole 34 of the plate 12. A regulation wheel 36whose toothing 38 meshes the worm screw 30, is rotationally mounted onthe pin 32. The regulation wheel 36 co-operates with a return spring 37which tends to rotate the rocker arm assembly around the axis 40 of thepin 32. The relative position of the wheel 36 with respect to the pin 32can be varied by turning the worm screw 30 and consequently varying thepre-load of the return spring 37.

[0015] In the assembled configuration, the inner plate 10 and the outerplate 12 form a cage structure which rotationally carries thetransmission wheels 14. The fact of using a metallic material for theinner plate 10 and a structural fiber fabric incorporated in athermoplastic resin for the outer plate 12 results in a situation whichis an ideal compromise in terms of reducing weight and maintainingstructural resistance with respect to the flexion stress, withoutcausing problems of interference with the spokes of the wheel in theposition in which the chain engages the pinion which is closer to thewheel.

What is claimed is:
 1. A rocker arm assembly for a rear derailleur of abicycle, the assembly comprising an outer plate having a pivot pin, aninner plate and a pair of idle transmission wheels arranged between theouter plate and the inner plate, wherein the inner plate is made ofmetallic material and the outer plate is made of a structural fiberfabric incorporated in a plastic material matrix.
 2. The rocker arm ofclaim 1, wherein the plastic material is a thermo set.
 3. The rocker armof claim 1, wherein the plastic material is a thermoplastic.
 4. Therocker arm of claim 1, wherein the fabric is a carbon-based fabric. 5.The rocker arm of claim 1, wherein said pivot pin carried by the outerplate is made of metallic material and is fastened to the outer plate bycaulking.
 6. The rocker arm of claim 1, wherein the outer plate includesan integral element made of a plastic material projecting from an outerface of the plate which carries an adjustment screw co-operating with awheel rotationally mounted on said pivot pin.
 7. The rocker arm of claim1, wherein said outer plate has a cross-sectional profile whichessentially has a shape of a shallow channel.
 8. The rocker arm of claim1, wherein the outer plate is obtained by compression molding.
 9. Arocker arm assembly for use on a rear derailleur of a bicycle, theassembly comprising: an inner plate, made of a rigid metallic material,including first and second tapped holes; an outer plate having a pivotpin, made of a plastic composite material, including first and secondthrough apertures respectively aligned with the first and second tappedholes, and connected to the inner plate via fasteners passing throughthe first and second through apertures and first and second tappedholes; and first and second idle gears positioned between the inner andouter plates and aligned with a respective one of the first and secondthrough apertures.
 10. The rocker arm assembly of claim 9 wherein thecomposite material is structural fiber fabric incorporated in a plasticmaterial matrix.
 11. The rocker arm assembly of claim 10 wherein theplastic material is a thermo set, and the composite material iscompression molded.
 12. The rocker arm assembly of claim 9 wherein themetallic material is aluminum alloy.
 13. The rocker arm assembly ofclaim 9 wherein the outer plate further includes an essentially U-shapedcross section.
 14. The rocker arm assembly of claim 13 wherein the outerplate further defines a plurality of apertures therethrough.
 15. Abicycle derailleur rocker arm assembly comprising: a rigid metallicinner plate having first and second tapped holes; a plastic compositematerial outer plate having first and second through aperturesrespectively aligned to oppose the first and second tapped holes and apin which extends away from the inner plate; first and second idle gearspositioned between the inner and outer plates and aligned with arespective one of the first and second through apertures; fastenerspassing through the first and second through apertures and engaging arespective one of the first and second tapped holes; a regulation wheelmounted on the pin; and a return spring that connects with theregulation wheel and rotates the assembly about the pin.
 16. Theassembly of claim 15 wherein the composite material is comprised of astructural fiber fabric in a plastic matrix.
 17. The assembly of claim16 wherein the plastic matrix is a thermo set.
 18. The assembly of claim15 wherein the composite material is compression molded.
 19. Theassembly of claim 15 further comprising a worm screw for varying thereturn spring's tension.
 20. The assembly of claim 15 wherein the outerplate further includes an essentially U-shaped cross section.
 21. Theassembly of claim 15 wherein the metallic material is an aluminum alloy.